A current wireless communication system, such as a code division multiple access system and a wideband code division multiple access system, generally adopts a variable envelope modulation technique to perform amplitude modulation and phase modulation. In the variable envelope modulation technique, a power amplifier is required to perform signal amplification, and this kind of modulation technique enables an envelope signal to have a wider dynamic range, and bandwidth often reaches more than dozens of megahertz (MHz); therefore, high requirements is required on the bandwidth and gain performance of the power amplifier, and the power amplifier needs to have higher bandwidth and a flat gain curve.
Due to the Miller effect of a power stage, the gain frequency characteristic and bandwidth of the conventional power amplifier are greatly affected, the gain curve is not flat, and the response of the high-bandwidth power amplifier to a large signal tends to be unstable, thereby limiting the bandwidth range.